The present invention relates in general to improvements in composite photography systems of the type in which different scenes are photographed by separate cameras and these scenes are combined to form the finished picture. More particularly, the present invention pertains to new and improved motion synchronizing means between two or more cameras wherein the movement of the perspective viewpoint of one camera in relation to the scene it is seeing is sensed and related to the perspective viewpoint of another camera in relation to the scene it is seeing.
The combining of scenes viewed by separate cameras is generally accomplished by a process in which the portions of the background scene photographed by the background camera corresponding to the foreground objects are blanked out or masked in the foreground scene photographed by the foreground camera. In the film technique currently in use, the masking is accomplished by making an opaque matte of the foreground objects and printing the background scene masked by that matte. The foreground objects are then printed on the masked areas of the background to form the composite picture. The cameras may be either film or television cameras. The foreground scene typically includes moving objects such as actors. Because the masking matte moves or travels from frame to frame, such a system has come to be referred to in the art as a traveling matte system.
A major problem in such a system is to maintain registration of the perspective viewpoints of the background and foreground cameras within acceptable accuracy during relative movement of the foreground and background cameras in relation to the objects constituting their frame of reference, including the scene which each views. Unless this registration is maintained, the desired illusion is lost. The required degree of accuracy depends upon the intended use of the finished composite picture. Wide screen motion picture projection, for example, requires much more accurate registration than commercial television.
Up to very recently, composite image systems, such as traveling matte systems, have not provided the capability of synchronized movement of the cameras relative to their respective frames of reference, including their viewed scenes. The system described in two U.S. patents, one issued to Dan Slater, Oct. 21, 1975, for an Optical Node Correcting Circuit, U.S. Pat. No. 3,914,540, and another one issued to Douglas H. Trumbull, et al., for Composite Photography System on Sept. 2, 1975, U.S. Pat. No. 3,902,798, describe a system which has the capability of synchronizing the background camera movements with the foreground camera movements in the x, y, z, yaw and pitch axes so that a cameraman can "dolly," "crab" or "pedestal" as ordered by the director in the foreground to achieve the desired artistic effect while the background camera tracks the movement of the foreground camera in these five axes. For a complete description of such a system, reference should be made to these two patents. They are incorporated herein as if fully set forth at this point.
As explained in these patents, the objects viewed by the perspective of the two cameras usually differ in scale or relative size. The scene viewed by the background camera typically could be a miniaturized set while the scene viewed by the foreground camera typically would be a life-size actor or object. Combining a life-size actor with a miniature background set, according to the traveling matte technique, will cause the full-size actors to appear to be in a lifelike environment of the miniaturized set. Because the scene viewed by the background camera is miniaturized, the movements of the background camera are appropriately scaled to the size of the miniature set. This is fully explained in the above two patents. It should be borne in mind that this technique, however, is not limited to a situation where life-size actors are placed into a miniature set. It also finds application in the remote control of cameras generally such as where, for example, the environment of one or both of the cameras controlled is adverse by being dangerous, relatively inaccessible or the like.
Typically, the foreground camera is mounted on a four-wheel dolly which is steered by an operator while the cameraman rides thereon and shoots the scene being filmed. The dolly is driven and steered by means of all four wheels, wherein all four wheels pointed in the same direction at one time to provide a constant heading. It is, therefore, capable of moving along the ground plane or stage floor in a limitless variety of travel paths. The position and perspective in which the foreground camera views its scene is duplicated with great accuracy and effectiveness in the background camera along the x, y, z, yaw and pitch axes, as fully explained in the two above-identified patents.
However, prior art systems that utilize a dolly-mounted foreground camera have failed to recognize, and compensate or correct for inherent rotational movement of the dolly about its vertical axis which is generally perpendicular to the x-y axis, ground plane or stage floor.
It has been found that the following factors affect dolly rotation about its vertical axis during a dolly move:
1. stretch or shock in the dolly steering mechanism;
2. unevenness of the stage floor (x-y plane) on which the dolly moves; and
3. dolly tire slippage.
None of these factors can be controlled to the point of reducing dolly rotation to an acceptable level without restricting dolly maneuverability, as would be the case, for example, if the dolly was mounted for movement along a physical track. The failure to recognize and correct for the problem has resulted in unrealistic movement of the foreground objects in the background scene when the two scenes are combined.